The organic thin-film solar cell is a solar cell comprising an organic thin-film semiconductor composed of a combination of conductive polymer, fullerene, etc. The organic thin-film solar cell can be produced by a convenient process including the coating or printing of a photoelectric conversion film, so that the production cost thereof can be lower than that of a solar cell based on an inorganic material, such as silicon, CIGS, CdTe or the like. However, the photoelectric conversion efficiency and life of the organic thin-film solar cell are inferior to those of conventional inorganic solar cells. A reason therefor would be that the properties of an organic semiconductor for use in the organic thin-film solar cell are susceptible to parameters whose control is difficult, such as the purity, molecular weight distribution, orientation, etc. of semiconductor materials. Accordingly, various innovations for enhancing the power generation efficiency of the organic thin-film solar cell are required.